The present invention relates to an azinphos-methyl powder insecticide composition, and a process for preparing the composition, that reduces or eliminates the tendency of the azinphos-methyl composition to deflagrate and undergo exothermic decomposition.
Insecticides for open areas are generally applied by spraying. Sprays can be produced by either diluting liquid concentrates or by adding liquid to an insecticide in wettable powder form. The dry powder form of insecticides is generally preferred over the liquid form because it is less likely to penetrate the clothing and skin of the person handling it than a liquid concentrate. It is also easier to clean up a powder than a liquid in the event of a spill. However, azinphos-methyl in powder form is sensitive to heat. An ignition source could result in deflagration of the powder. As such, there is a need to make the powder forms of azinphos-methyl less likely to deflagrate without adversely affecting other desirable properties, such as storage stability.
A form of insecticides useful for treating enclosed, limited spaces is a fumigant. Japanese Patent 63,039,803 teaches an insecticide fumigant that undergoes controlled decomposition. In this fumigant, the insecticide is mixed with a thermodecomposable compound that will produce nitrogen and carbon dioxide at temperatures less than 300.degree. C. Among the thermodecomposable compounds taught to be appropriate are ammonium salts, metal azides, inorganic carbonates and organic carboxylic acids. These thermodecomposable compounds are used in quantities such that they constitute at least 50% by weight of the fumigant mixture.
U.S. Pat. No. 5,268,177 teaches a process for raising the temperature at which deflagration of azinphos-methyl occurs by adding thereto a carbonate of alkali metal in an amount such that the carbonate is at least 10% by weight of the total mixture. The resultant mixtures are characterized by a reduced tendency toward deflagration at temperatures below 200.degree. C. Examples 5 and 6 of Patent 5,268,177 illustrate comparative azinphos-methyl formulations in which magnesium sulfate and magnesium sulfate heptahydrate, respectively, were substituted for the carbonate or bicarbonate. The magnesium sulfate and the magnesium sulfate heptahydrate each constituted approximately 25% by weight of the azinphos-methyl formulations in Examples 5 and 6, respectively. Deflagration (manifested by smoke generation) of both the Example 5 and 6 formulations occurred at a temperature of 188.degree. C.